USDA Zones indicate minimum annual temperature; the information we really need to help answer your question is when does your last frost typically occur?
In Zone 7, your expected low temperatures would be about 5°F (Z8 more like 15°F), but this doesn't help us know when you expect the weather to start warming up -- which is the key consideration here.
I did a quick check of frost dates on the Farmer's Almanac, and I see that Baltimore is typically April 11th. My answer below is based on that.
For transplants, I might try spinach, lettuce and kale. You could probably plant these in February if you're using row covers. Depending on soil temperature (see below), I might wait 2-4 weeks, though. Most of your greens can go out relatively early -- beets and chard can be seeded a couple of weeks before frost-free as long as the soil has warmed up, for example. Carrots don't mind being seeded a little early. And the general advice on peas is to plant them "as soon as the ground can be worked", but again consider soil temperature and germination time.
Your limiting factor in the early season may be the amount of sunlight that the plants actually receive during the day; in February the sun is probably still fairly low in the sky in your area? Thus planting out might not really gain you any jump on harvest -- though it might be good enough for your mental health to be able to get outside in the late winter that it's worth the effort even if you don't get anything to eat any earlier...
The big limitation on direct-seeding will be soil temperature. Most seeds won't germinate (or will do so very slowly) when the soil temperature is below 60-70°F. Peas (for example) are more tolerant of colder soil, but will still germinate much more slowly at 50°F than at 65°F.